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Underwater repairs to, and rehabilitation of, existing reinforced concrete velocity caps of the circulating water intake structure at St. Lucie Powerplant, Fort Pierce, Florida were made utilizing high-performance in a marine environment. Use of this repair technique avoided the necessity of constructing a cofferdam for repair work in the dry, and thus minimized interruption to plan operation, and resulted in considerable savings. Mix proportions for the high-performance concrete included cement, fly ash, silica fume, and antiwashout admixtures as well as high-range water-reducing and set-retarding admixtures. The mix proportions were tested extensively in the laboratory and field conditions to optimize the slump and the initial setting time of concrete while assuring early compressive strength requirements for conformance with the specified requirements. Large scale mock-up tests, utilizing both tremie and pumping methods, were conducted to simulate under water placement in the surf zone and to select the actual concrete placing method, rate of placement, and to identify surface preparation and protection requirements. Construction procedures for the new reinforced concrete slabs involving approximately 3000 yd 3 precast and tremie concrete utilizing a barge-mounted concrete batch plant; quality control and post-placement inspection measures are also discussed.

A super-workable concrete, which has excellent deformability and resistance to segregation and can be filled into heavily reinforced formwork without vibrators, was developed. This new type of concrete is made not only with the general materials for concrete such as ordinary portland cement, aggregates, water, and air-entraining water-reducing agent, but also with blast-furnace slag, fly ash, superplasticizer, and a newly developed viscosity agent. When the slump of this super-workable concrete is tested, diameter of the flow is more than 60 cm. Since the super-workable concrete has excellent durability as well as superior filling ability, it should be a proper concrete for projects under severe conditions. The super-workable concrete was employed in the construction work of a 20-story building. It was placed in the center-core from the basement to the third floor. The building was designed as a hybrid structure, in which the reinforced concrete core was surrounded by the steel structures. The specified design strength of the concrete was 480 kgf/cm 3 (47.1MPa). The greatest nominal diameter of deformed bars was 51 mm, and they were very congested. The super-workable concrete was produced in ready mixed concrete plants near the construction site, and 1500 m of the super-workable concrete was placed successfully. Through this project it was confirmed that the super-workable concrete can be supplied from general ready mixed concrete plants with practical care of quality control in materials.

Three types of High Performance Concrete (HPC) for highway applications were investigated: Very Early Strength (VES), High Early Strength (HES) and Very High Strength (VHS). Two of the objectives of the research were to measure the chloride permeability of these concretes and explore an alternate method using AC impedance. Many of the concretes had coulomb values of 4000 and higher, placing them in the "high permeability" category as specified by AASHTO T 277 - Rapid Chloride Permeability Test (RCPT). Coulomb values were also found to decrease with concrete age and with increased silica fume content. Coulomb values were found not to vary significantly with dosage of calcium nitrite used as accelerator, up to 6 gal/yd 3 (29.7 l/m 3). The AC impedance test results (ohms) were found to correlate well with the RCPT results (coulombs) and were sufficiently accurate to place the concretes in the proper chloride permeability category. The advantages of the AC impedance test are that it is faster and less expensive than the RCPT and it avoids the potential heating problem sometimes encountered in the RCPT. AC impedance was found to increase with concrete age and with increased silica fume content and decrease with increased calcium nitrite dosage.

In 1989, the Strategic Highway Research Program contracted with North Carolina State University to investigate the use of High Performance Concrete in highway applications. A major goal of this research project was to determine if HPC mixtures could be successfully produced in the field. In addition, an evaluation was to be made of the long-term performance of this material under field service conditions. Five field installations were constructed around the country for this purpose. The fresh and hardened properties of the concrete were found to be generally acceptable at each site. Some cracking has developed in a few sections. A set of recommendations with regard to the use of HPC in the field was developed as a result of the field work.

The cable-stayed bridge which is being built across the Elorn river near Brest (western France) will have the world's longest span (400 m, or 437 yd) in this range of full concrete bridge. Besides a normal-strength concrete (C 35/6,500 psi), a lightweight concrete (LC 32/4,600 psi) is extensively used in the deck, in order to minimize the effect of dead load on the overall stability. But the most significant part of the loads to be carried by the bridge is due to the wind, with a maximum accounted speed (in the design) of 210 km/h (130 mph). Furthermore, the bridge is located about 3 km (2 miles) from the sea; thus, the wind will carry a large amount of chlorides. This is why the term serve environment seems to be appropriate for the Elorn bridge. Two grades of high-strength concrete--namely C60/ psi and C80/ psi--are used in the towers. For the first time in France--and perhaps in the world--a strength of 80 MPa (11,600 psi cylinder strength) has been used in the design of a bridge. Details on the concrete mix proportions, producing facilities, placing techniques and testing of samples are given in this paper. A special emphasis is put on the thermal curing aspects. As the thickness of the towers walls is 1.10 m (3.5 ft), the temperature can reach more than 80 C in the pylons. The effect of heat of hydration on the long-term strength and modulus was investigated. Also, finite-element calculations were performed, in order to predict the stresses induced by thermal gradients, and to choose the most appropriate curing (thermal insulation, time of form removal, and so on).